Rihanna may be pushing herself a little too hard. The superstar had to cancel yet another stop on her Diamonds World Tour earlier this week because she doesn't know when to rest.

In an Instagram post, the 25-year-old explained that she's been sick for a while now. "I was sick since San Diego! I kept working cuz i thought 2 days off after the Vegas show would be enough time to recover and I f---ed up," she wrote. "Those were 2 days off from hell and today is no different! I'm sad and disappointed about it!! I had all kinds of plans for Houston!!!"

Meanwhile, pics are circulating of Rih spending down time with her loves — celebrating her best friend's birthday in Las Vegas over the weekend and shopping with Chris Brown in L.A. — fueling speculation around just how sick she is. Pics also showed, however, that she was spotted leaving a doctor's office in Beverly Hills yesterday.

The doctor's visit is fanning the flames of a rumored secret pregnancy.

With a dozen more tour stops to go, starting with Tampa, FL, this Friday (April 19), she doesn't have much time to pull it together.

Get well soon Rih Rih. 

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(photo: Winston Burris/WENN.com)